You don't really need any sort of anti-virus or ad protection on an android if you download APK's from only the play store. Risk of your device being exploited through the web is just so unlikely for everyday users, but if you really do need anti-virus on a phone i'd say Emsisoft is a good choice. Try using a different/Alternate browser to the default though. E.G. Aloha Browser. Also, make sure you're always on a proxy/VPN. It may decrease your speed but the extra protection is much required